Sheets for household use are well known in the art. It is often desired to decorate such sheets, such as by printing. Printing imparts an aesthetically pleasing pattern to the sheet. Alternatively, the sheet may be embossed to impart an aesthetically pleasing pattern which is also tactually discernible.
Such sheets are typically made in continuous form, then later cut to discrete lengths as desired. Such cutting to discrete lengths may occur at the point of use, such as is caused by the consumer detaching one sheet from the balance thereof at a line of termination. For this purpose, the line of termination typically comprises a line of weakness, such as a perforation. Alternatively, the continuous sheet may be cut into discrete portions prior to the point of use. Such an arrangement often occurs in individual napkins which are cut during manufacture and purchased by the consumer as discrete units.
It has been relatively facile in the prior art to register indicia with the cross machine direction of such sheets while such sheets are transported in a continuous fashion during manufacture. However, it is more difficult to register the indicia in the machine direction, and particularly difficult to register the indicia with lines of termination.
One manner with which the foregoing difficulty has been addressed is by keeping the length of the sheet of the continuous sheet path between the point at which the indicia are applied and the point at which the lines weakness are imparted to the sheet relatively short. However, this approach does not provide for feasibility in the manufacturing process, requires smaller sized equipment, and is simply infeasible where the modules necessary to impart the lines of weakness or apply the indicia themselves comprise a web path which is large enough to cause improper spacing between the indicia and the lines of weakness.
Another attempt to address this difficulty has been to keep the length of the path relatively short between the point at which the latter of the indicia and the lines of termination are applied or imparted, respectively, to the continuous sheet and the point at which the continuous sheet is cut to separate it into a discrete unit at the point of manufacture. This approach works well where relatively short discrete sheet lengths are desired, as for example with an individual table napkin.
However, this approach is infeasible where a relatively longer sheet length is desired as, for example, with a roll product, such as toilet tissue or paper toweling. Such difficulty is due to the cumulative error which occurs over the length of the continuous sheet between the point at which the indicia are applied and the lines of perforation imparted to the sheet. By way of example, if a misregistration of 0.001 inches occurs at a first repeating unit of the continuous sheet a misregistration of one inch will occur after 1,000 inches of sheet are manufactured.
For example, referring to FIG. 1, the cumulative error of discrete napkins, each having a machine direction length of about 12 inches is about 0.125 inches. Conversely, the prior art cumulative error over 700 inches of continuous sheet, as for example the approximate length of an ordinary roll of paper toweling, is about 0.5 inches. This greater cumulative error makes it infeasible to use prior art processes to manufacture such rolls of paper toweling.
An even bigger problem occurs in the prior art when the parent roll is exhausted and a new parent roll started. The parent roll is the large roll of product later converted to multiple individual sheets by the apparatus and process disclosed herein. Different parent rolls have different properties which affect the transport of the sheet through the apparatus. For example, the amount of stretch in the sheet as it travels through the apparatus frequently varies greatly between parent rolls. As these properties vary, so does the registration of the indicia with the lines of termination. Such variations in registration must be accounted for in the manufacturing process.
Each vertex of the two graphs in FIG. 1 represents a chop-off cut, where the sheet is cut into a discrete unit from the succeeding sheet. The greater length of the paper toweling sheet results in proportionally greater cumulative error in the sheet.
As used herein, a “unit” is defined as that portion of the sheet which is discrete as delivered to the consumer, as, for example, a single table napkin or a single roll of paper toweling or toilet tissue. It will be apparent that the length of the paper toweling or toilet tissue is significantly greater than the length of the discrete table napkin. The cumulative error will, of course, be greater in the paper toweling or toilet tissue, in an amount proportional to the difference in sheet length.
Accordingly, approaches which are feasible when dealing with discrete articles of relatively short unit length are not sufficient for dealing with registration difficulties which occur in longer sheet lengths. Sheet length is defined as the length of the product, taken in the machine direction, as presented to the consumer. For example, the sheet length of a discrete napkin or placemat is the machine direction length of one napkin or placemat. The sheet length of a roll of perforated paper toweling is the machine direction length of the entire roll, taken from the point of core attachment to the tail seal.
It is therefore an object of this invention to provide a mechanism for overcoming the problems associated with misregistration between indicia and lines of termination in products having longer unit length, and more particularly in core wound paper products, presented to the consumer in roll form. It is also an object of this invention to provide for adjustment of such spacing while the sheet is being transported during manufacture.